In a common generator arrangement current is conveyed from winding ends to phase rings contained in a gas-cooled casing and then further connected to bushings used to convey the current through the casing wall. To convert the frequency of the generators multiple phases to grid frequency the bushings are further connected to semiconductor arrangements forming a separate frequency adaptation unit.
It is desirable to minimise the overall axial length of the generator and so the bushings are arranged so as to extend radially outward through the casing. The result is however a radially space inefficient design that requires complex bus ducts extending yet further outwards from the casing before being routed to a common point for connection to the frequency adaptation unit.
A partial solution to this problem, described in EP0707372, involves locating at least a part the frequency adaptation unit within the end casing so as to significantly decrease the number of required bushings thereby providing a more radially space efficient design. The arrangement is however disadvantaged in that the available space in the casing is limited and so access is poor making it difficult to check and replace components. When the generator is hydrogen cooled, further access limitations are imposed exacerbating this disadvantage. While the frequency adaptation parts in the casing can be cooled in conjunction with other generator components, in the case of hydrogen-cooled generators it is desirable to separately cool these parts, with for example deionized water, due to the amount of heat generated by the parts. However to do this inside a hydrogen-filled casing adds complexity and cost. Yet further, should the parts of the frequency adaptation unit fail e.g. by short-circuiting, they may explode. If this should occur inside the casing significant machine damage can occur.